clBuildProgram: refactor token append code
clBuildProgram: refactor token append code

The duplicate code to append a (valid) token to modded_options is
refactored into a macro, and the following two issues are fixed:

* a potential buffer overflow if the token length is bigger than 256 +
  whatever room is left in modded_options;
* a potential memory leak in case of reallocation failure.

franz/pocl,jrprice/pocl,dsandersimgtec/pocl,vkorhonen/pocl,pavanky/pocl,pocl/pocl,0charleschen0/pocl,jrprice/pocl,sting47/pocl,0charleschen0/pocl,sting47/pocl,Oblomov/pocl,0charleschen0/pocl,0charleschen0/pocl,sting47/pocl,pocl/pocl,Oblomov/pocl,maZZZu/pocl,pavanky/pocl,franz/pocl,jrprice/pocl,maZZZu/pocl,Oblomov/pocl,dsandersimgtec/pocl,pavanky/pocl,pocl/pocl,jrprice/pocl,sting47/pocl,Oblomov/pocl,franz/pocl,vkorhonen/pocl,dsandersimgtec/pocl,franz/pocl,vkorhonen/pocl,sting47/pocl,maZZZu/pocl,rjodin/pocl,pocl/pocl,rjodin/pocl,franz/pocl,rjodin/pocl,vkorhonen/pocl,pavanky/pocl,maZZZu/pocl,pocl/pocl,dsandersimgtec/pocl,Oblomov/pocl,rjodin/pocl